The effects on humans of the Chornobyl nuclear disaster in Ukraine 17 years ago have been widely studied. But little research has been done on the effects on wildlife in the contaminated region around the nuclear plant. Now, research by two Ukrainian scientists that shows worms in the affected area have changed their sexual habits has provoked some interest.

Prague, 29 April 2003 (RFE/RL) -- Research published by Ukrainian scientists who studied three types of worms in the nuclear-contaminated zone around Ukraine's Chornobyl nuclear-power plant has shown dramatic changes in the worms' reproductive habits.

Their research, published this month in two prestigious British scientific magazines, "The New Scientist" and "The Journal of Environmental Radioactivity," shows that the worms have started mating with each other instead of with themselves in a process called "asexual reproduction."

The scientists attribute the worms' new habits to a survival mechanism prompted by radioactive pollution, with the worms searching for mates in an attempt to increase the survival rate of their species.

The research is being hailed as one of the first pieces of evidence of how wildlife is affected by radioactive pollution. Scientists say that while there is plenty of evidence on the impact of radiation on humans, its effects on wildlife are still poorly understood. In the past, there have been no separate radiation-exposure limits set for wildlife because the assumption was that if humans were protected, wildlife would also be safe.

The research by Gennady Polikarpov and Viktoria Tsytsugina from the Institute of Biology of the Southern Seas in Sevastopol, Crimea, challenges that view. They compared the reproductive behavior of three species of worms living near Chornobyl with the same species 20 kilometers away.

Both sets of worms were living in the sediments of lakes with similar temperatures and chemical compositions. The worms in the Chernobyl Lake, however, received 20 times as much radiation as those in the other lake.

Polikarpov and Tsytsugina found that the worms increasingly chose to mate with other worms instead of with themselves. The scientists reasoned that the worms switched to sexual reproduction in an attempt to protect themselves from the radiation. Sexual reproduction, the theory goes, would allow natural selection to promote genes that offer better protection from radiation damage.

An expert on the effects of radiation and a writer for "The New Scientist" magazine, Rob Edwards, said the Ukrainian scientists have shown that radiation may have more subtle effects on wildlife than previously suspected.

"We've done lots [on the radiation's] effect on humans but there's relatively little [research] done on wildlife and what this work by Ukrainian scientists shows is that the radiation from Chornobyl does seem to be affecting the way in which worms reproduce and affecting it in quite a dramatic way," Edwards said.

Edwards hopes that the work of the Ukrainian scientists will prompt further studies on other forms of wildlife. "What the authors of the [Ukrainian] study say is that it implies or suggests that if you find the radiation from Chornobyl is affecting the way worms reproduce, obviously it could be affecting other forms of wildlife in other ways. It could be affecting the way other animals reproduce perhaps in more subtle ways and I think it shows it's very important to investigate those things further because really we simply don't know at the moment," he said.

The International Commission on Radiological Protection (ICRP) recommends radiation safety limits that are incorporated into regulations set by the International Atomic Energy Authority and the European Union.

ICRP scientific secretary Jack Valentin said the organization has not previously set limits for wildlife but is now consulting scientists and scientific bodies throughout the world to see whether there should be such limits.

"We're not proposing a regulatory system at this stage. We're saying this will have to be addressed and we will continue to work on this. We are saying that perhaps the way forward will be to have a reference for [animals] and look at various model species one can use. But there are certainly no limits at this stage," Valentin told RFE/RL.

He said the ICRP will look at the Ukrainian scientists' work as part of the organization's consideration of whether to set separate limits to protect wildlife.

Edwards of "The New Scientist" said the Ukrainian study is valuable evidence to rectify radiation regulations that have assumed that wildlife was affected by radiation in a similar way to humans.

"That sort of flaw in the way we've protected wildlife in the past has been recognized on an international level by most radiation scientists, so as a result of that there are a large number of studies beginning or under way looking at precisely this issue: how does radiation, particularly low levels of it, affect wildlife and how can we draw up standards to protect wildlife? So I think this study is the first of many," he said.

A scientist at the Dublin Institute of Technology, Carmel Mothersill, one of the experts helping the ICRP develop its new policy on protecting wildlife, called the Ukrainian explanation for the worms' sexual behavior "a plausible mechanism."